1. Field of the Invention
The present invention relates to a color translucent liquid crystal display panel made by providing color filters in a translucent liquid crystal display panel which is reduced in power consumption and is made capable of a reflection display to improve visibility when light (external light) in an external environment is strong, and also capable of a temporary transmission display by providing an auxiliary light source to improve visibility when the external light is weak.
2. Description of the Related Art
At present, as liquid crystal display devices using liquid crystal display panels, there are a transmissive liquid crystal display device having an internal light source, a reflective liquid crystal display device using light of an external light source, and a transflective liquid crystal display device using light of an external light source when it is bright and turning on an auxiliary light source when the external light source is dim to be used in a transmission state. The reflective liquid crystal display device is effective in order to reduce the power consumption of and to thin the liquid crystal display device. A reflection display, however, can not be recognized when the external environment is dark, and thus a transflective display is hopeful.
Such a conventional transflective liquid crystal display device is explained using FIG. 16. FIG. 16 is a view schematically showing a cross section of the transflective liquid crystal display panel in this liquid crystal display device. Incidentally, it is assumed that a visible side by an observer is the upper side.
This liquid crystal display panel includes a liquid crystal layer 15 sandwiched between a first substrate 1 and a second substrate 5 each of which is transparent. Further, the liquid crystal display panel has scanning electrodes 2 in stripes parallel to the paper surface, each made of an indium tin oxide (ITO) film which is a transparent conductive film, on the first substrate 1 (inner surface) provided on the viewer side. On the other hand, on the second substrate 5 (inner surface), a color filter 9 is provided which is constituted of red (R) filters 6, green (G) filters 7 and blue (B) filters 8. In this color filter 9, adjacent filters 6, 7 and 8 slightly overlap one upon another or abut on each other.
On the color filter 9, a protective insulating film 10 is formed to flatten levels of the color filters and prevent deterioration thereof. The protective insulating film 10 is provided thereon with data electrodes 11 in stripes perpendicular to the paper surface each made of an indium tin oxide (ITO) film that is a transparent conductive film. The scanning electrodes 2 and the data electrodes 11 are formed in directions perpendicular to each other to form pixel portions where they coincide as viewed in a plane view, and a plurality of the pixel portions form a display region.
Further, alignment films 12 are provided on the inner surface of the first substrate 1 including the scanning electrodes 2 and on the inner surface of the second substrate 5 including the data electrodes 11 respectively as treatment films for aligning the liquid crystal layer 15 in predetermined directions. The first and second substrates 1 and 5 are coupleed together with a fixed gap therebetween with a sealing material 16 so that the scanning electrodes 2 on the first substrate 1 and the data electrodes 11 on the second substrate 5 are opposed, a liquid crystal is injected from an opening (not shown) provided in the sealing material 16, and sealed with a closing material (not shown), thereby forming the liquid crystal layer 15.
Furthermore, a first polarizer 21 is provided on the visible side (upper side) of the first substrate 1, and a second polarizer 22 is provided on the opposite side (lower side) to the visible side of the second substrate 5. On the lower side of the second polarizer 22, a transflective reflector 24 is provided which transmits a part of light and reflects almost all the remaining light. Moreover, a light source portion 31 is provided below the transflective reflector 24 as an auxiliary light source. The light source portion 31 is constituted of, for example, a cold-cathode fluorescent tube, a reflector, a prism sheet and a diffuser.
In such a transflective liquid crystal display panel, light from the outside, for example, passes through the first polarizer 21 and the first substrate 1 as a first incident light 35, and is then made incident on the liquid crystal layer 15. The liquid crystal layer 15 causes optical rotation or phase difference, and the light is made incident on the color filter 9, passes through the second substrate 5 and the second polarizer 22, and reaches the transflective reflector 24. The first incident light 35 passes through such an optical path and is thus absorbed by the aforesaid members, resulting in attenuation of the light incident on the transflective reflector 24. The path of light is explained in relation to major constituents, and additionally the scanning electrodes 2 and the like actually cause absorption.
The first incident light 35 is reflected by the transflective reflector 24 and goes out to an observer side as a first reflection light 36, while absorbed by the second polarizer 22, the second substrate 5, the color filter 9, the liquid crystal layer 15, the first substrate 1 and the first polarizer 21. Therefore, the first reflection light 36 passes through the color filter 9 twice, and thus it is greatly absorbed by the color filter 9.
On the other hand, other light component from the external light source, as a second incident light 37, passes through a path similar to that of the first incident light 35 to reach the transflective reflector 24. The second incident light 37, which is a component passing through the transflective reflector 24, is slightly reflected by the constituent of the light source portion 31 disposed below the transflective reflector 24. This reflection light goes out as a second reflection light 38, but it becomes extremely weak reflection light because it is originally weak reflection light, and additionally, only a component of the light passes through the transflective reflector 24 when passing through it again, and it is absorbed by the constituents including the color filter 9.
As described above, when the external light source is used, the first and second incident lights 35 and 37 passes through the color filter 9 twice and go out to the observer side as the first and second reflection lights 36 and 38 to be recognized as a display.
In contrast to the above, emitted light from the light source portion 31 disposed below the second substrate 5 becomes a transmission light 40 which passes through the transflective reflector 24, the second polarizer 22, the second substrate 5, the color filter 9, the liquid crystal layer 15, the first substrate 1 and the first polarizer 21 to go out to the observer side. Accordingly, the transmission light 40 passes through the color filter 9 only once.
Consequently, brightness is important only in the case of the reflection display because the light going out to the observer side passes through the constituents twice and is thus absorbed greatly. It is particularly desired to use a color filter with little absorption because the light passes through the color filter twice.
Spectral characteristics of the color filter are explained here using FIG. 17. FIG. 17 is a graph showing spectral characteristics of the R, G and B color filters.
In FIG. 17, the horizontal axis represents optical wavelength in the unit nanometers (nm), and the vertical axis represents transmittance in the unit percent(%).
The spectral characteristic of the R, G and B filters used in the reflective liquid crystal display panel are represented by curved lines 66, 67 and 68, respectively. For example, the red (R) filter is required to have a high transmittance in a range from 600 nanometers (nm) to 800 nanometers (nm) as shown by the curved line 66 (chain line). Further, brightness is important as described above, and thus the red (R) filter is required to have a transmittance of about 40% also in a wavelength region of blue or green which is shorter than 600 nanometers (nm).
Similarly, the green (G) filter is required to have a high transmittance in a range from 500 nanometers (nm) to 600 nanometers (nm) as shown by the curved line 67 (solid line), and is required to have a transmittance of about 40% also in other wavelength region. The blue (B) filter is required to have a high transmittance in a range shorter than 500 nanometers (nm) as shown by the curved line 68 (broken line), and is required to have a transmittance of about 40% also in other wavelength region.
In contrast to the above, in the case of the transmission display, light passes through the color filter only once, and thus the above-described color filter used in the reflective liquid crystal display panel greatly decreases in chroma. Therefore, a color filter is employed, giving priority to chroma, in which its R, G and B color filters have spectral characteristics exhibiting high transmittances in narrow ranges (transmission wavelength regions), and exhibiting extremely low transmittances at other wavelengths as shown by curved lines 69, 70 and 71.
Because of the great difference in spectral characteristics of the color filter required in the reflection display and the transmission display as described above, the transflective liquid crystal display panel for performing both the reflection and transmission displays can not employ the color filter which satisfies both the requirements, presenting a problem that the display quality is necessarily decreased.
Further, formation of a region between the electrodes where the transmittance of the liquid crystal can not be controlled allows transmission light to leak from the region, decreasing display quality. Therefore, the region is normally shielded from light using a black matrix having a light shielding property. However, the use of the color filter having the black matrix for the reflective liquid crystal display panel decreases the reflectance in the black matrix region, presenting a problem of occurrence of a decrease in brightness.
In order to solve the above problems, there is a so-called front lighting method in which the light source portion is not provided below the second substrate, but light is introduced from around the first substrate to apply the light from above the first substrate. When the light is used as the light source for the reflection display, a light guide plate disposed above the first substrate 1 decreases display quality. Further, light made incident on the liquid crystal display panel is poor in uniformity, resulting in a display with nonuniform brightness.
Moreover, in the front lighting method, the light guide plate requires a thickness of several millimeters (mm) or more. Accordingly, when an input is conducted on a screen of the liquid crystal display panel, the display and an input portion are deviated from each other depending on a viewing angle due to the thickness of the light guide plate, presenting a problem in operability.
An object of the present invention is to solve the above-described problems and to provide a liquid crystal display panel capable of performing a bright display with excellent chroma either for a reflection display or for a transmission display.
In order to attain the above object, the present invention provides a liquid crystal display panel structured as follows.
A first substrate is provided on a visible side; a second substrate is provided opposed to the first substrate; a liquid crystal layer is sandwiched between the first substrate and the second substrate; a first color filter is provided on the first substrate or on the second substrate; a transflective reflector for transmitting a part of light and reflecting almost all the remaining light is provided on the opposite side to the visible side of the first color filter; and a second color filter is provided on the opposite side to the first color filter with respect to the transflective reflector.
In such a liquid crystal display panel, it is preferable to provide a transmitting hole portion with a high transmittance and a reflecting portion with a high reflectance in the transflective reflector.
Further, in this case, it is preferable that when signal electrodes are provided on the first substrate, and opposed electrodes are provided on the second substrate to form pixel portions where the signal electrodes and the opposed electrodes coincide as viewed in a plane view, the transmitting hole portion of the transflective reflector is provided inside the pixel portion.
Further, it is preferable that the second color filter is constituted of filters of a plurality of colors and is provided with overlapping portions where the filters of adjacent colors overlap one upon another are provided between the pixel portions.
Furthermore, it is preferable that the first color filter is also constituted of filters of a plurality of colors and is provided with overlapping portions where the filters of adjacent colors overlap one upon another are provided between the pixel portions.
Alternatively, it is possible to provide a transflective reflector removed portion without providing the transflective reflector around a display region constituted of a plurality of the pixel portions.
In this case, it is preferable that the filters of different colors are arranged in the first color filter and the second color filter within a region of the transflective reflector removed portion.
Alternatively, the second color filter may be formed by laminating the filters of a plurality of different colors within a region of the transflective reflector removed portion.
It is also possible to provide a light shielding member having a reflectance lower than that of the transflective reflector and a light shielding property on the first substrate or on the second substrate within a region of the transflective reflector removed portion.
It is preferable that the transflective reflector has irregularities on a front face thereof and has a light diffusing property.
It is preferable to provide the transflective reflector on a surface on the visible side of the second substrate.
In this structure, it is preferable to provide the second color filter and the transflective reflector on a surface on the visible side of the second substrate in an order of the second color filter and the transflective reflector from the second substrate side.
Alternatively, it is also possible to provide the transflective reflector on the opposite side to the visible side of the second substrate, and the second color filter on the opposite side to the second substrate with respect to the transflective reflector.
It is possible that the second color filter is provided contacting a surface on the opposite side to the visible side of the transflective reflector.
It is preferable that the first color filter and the second color filter have substantially the same pixel pitch.
Further, it is preferable to arrange these color filters so that the filters of the same color coincide as viewed in a plane view.
It is preferable that the transflective reflector is a reflector having an optical polarizing property.
Further, it is preferable that the first color filter and the second color filter have aligning marks respectively.
It is also possible to provide a light shielding layer between the color filters constituting the second color filter.
It is also possible to provide a first polarizer on the visible side of the first substrate, a second polarizer on the opposite side to the visible side of the second substrate, and a white diffuser between the first substrate and the first polarizer.
It is possible to provide switching elements on the liquid crystal layer side of the second substrate, wherein the switching element and the transflective reflector are connected.
The liquid crystal layer may be constituted of a scattering liquid crystal, in which an ultraviolet cut film for absorbing or reflecting ultraviolet light is preferably provided on the visible side of the first substrate, and the second substrate is preferably constituted of a transparent plastic substrate or plastic film substrate.
In the liquid crystal display panel thus structured, incident light passes through the first color filter twice to go out to the visible side when the reflection display is performed, and emitted light from the light source passes through the second color filter and the first color filter once to be emitted to the visible side when the transmission display is performed.
Therefore, by using a first color filter having spectral characteristics giving priority to brightness for the reflection display and a second filter having spectral characteristics giving priority to chroma for the transmission display, the chroma when the transmission display is performed can be improved without expense of the brightness when the reflection display is performed. Consequently, display quality can be improved in both the reflection display and the transmission display.
The provision of the reflecting portion and the transmitting hole portion in the transflective reflector facilitates the control of the transmittance and the reflectance, and enables the control of the transmittance without changing wavelength dependency of the transmittance.
Further, the provision of the overlapping portions in the color filter enables improvement in contrast as in the case of the block matrix being provided without increasing the number of processing steps or complicating the structure.
The contrast can also be improved by providing the transflective reflector removed portion and covering it with the color filters of a plurality of colors or the light shielding member, and these members can be used as panel covers, thus omitting the step of forming a panel cover.
Further, the transflective reflector is provided on the opposite side (lower side) to the visible side of the second substrate, and the second color filter is provided on the lower side of the transflective reflector, thereby carrying out the present invention with little change in structure of the conventional liquid crystal display panel.
The second color filter and the transflective reflector, which are provided on the visible side (upper side) of the second substrate, can be located closely to the first color filter, thereby preventing occurrence of parallax and decreases in color purity and brightness.
The pixel pitches are made substantially equal and arrangement of colors are made the same in the first color filter and the second color filter, thereby enabling prevention of color mixture. Further, the provision of the white diffuser on the upper side of the first substrate enables improvement in viewing angle characteristics.
It is especially effective to use a material having polarizing characteristics for the transflective reflector in the case of the liquid crystal display panel using the polarizer and the transflective reflector because it is possible to decrease the gap between the first color filter and the second color filter and to thin the liquid crystal display panel.
Moreover, since the mutual positional relation between the first color filter and the second color filter is important, it is effective to provide the aligning marks enabling mutual alignment.
The above and other objects, features and advantages of the invention will be apparent from the following detailed description which is to be read in conjunction with the accompanying drawings.